The Cerro Prieto Project is an open-pit mining development in progress owned and operated by Minas de Oroco Resources, S.A. de C.V. (Oroco), a wholly owned subsidiary of Goldgroup Mining, Inc.
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Summary:
The local area, including the Project, consists of terrigenous shallow marine to deltaic clastic sediments equivalent to the Baucarit Formation (Nourse, 1995). Generally, this formation comprises polymictic conglomerates that are partly consolidated and cemented within a medium-grained matrix. These rocks can be observed on the north side of Cerro Prieto, where they form a discordant contact with the Cretaceous sediments and intrusions; however, they are otherwise rare in the Project area. Within the Project, these Tertiary sediments consist of thinly bedded fine to medium-grained arenites, exhibiting a general strike of 55° and a general dip of 30° to 45° to the northwest. Additionally, they are weakly metamorphosed and highly silicified.
Within the Project, Tertiary volcanic rocks include felsic volcanoclastics and andesitic to basaltic flows with minor rhyolite. They are disconformable located between the Tertiary arenites and polymictic conglomerates. In some areas, extensive rhyolite and dacite tuff beds have been deposited. Dyke rocks composed of andesite porphyry are present in the central part of the Project area.
The Reyna Deposit is situated along the northern extension of the active Esperanza Deposit open pit. Exploration has identified gold mineralization within a shear zone trending NW75–85°SE, extending for at least 150 meters. This zone exhibits intense supergene alteration, high concentrations of iron oxides, and hematized points that indicate leached sulfides, primarily sphalerite (ZnS) and pyrite (FeS2). Moderate amounts of crustiform and chalcedonic quartz represent the most recent SiO2 event. Gold anomalies range from 0.25 to 25.27 g/t.
Gold anomalies at the Coatí Deposit range from 0.2 to 6.65 grams per ton (g/t), while the Cata Zone exhibits anomalies between 0.2 and 18.83 g/t.
Two mineralization stages have been identified, Amorphous Milky Quartz and Quartz Druses.
Oxidation features include hematite, manganese, fine sulfides, and oxidized pyrite box-works.
Orientation: NW-trending structures dipping 50°–75° NE.
Gold Anomalies:
- Coatí: 0.2 to 6.65 g/t Au.
- Cata: 0.2 to 18.83 g/t Au.
Dimensions
The observable mineralized structure measures from 8 to 10 meters wide and extends from 40 to 50 meters from its outcrop to the boundary between Rancho Padres and Ejido Cucurpe.
Mineral Deposit
Mineral deposits at the Cerro Prieto mine site and surrounding areas are classified as low to intermediate sulfidation epithermal systems of silver and gold. These deposits are typical of many local occurrences in northeastern Sonora.
Local groundwater dilutes and cools, mixing with upwelling magmatic-derived hydrothermal brines in an extensional setting related to local rifts or detachment faulting associated with evolving metamorphic complex formation. Due to episodic events, mineralization typically deposits as multi-zoned veins, stockwork, and breccia. Deposit formation occurs in near-surface environments, usually between 200 m and 600 m, extending to a one-kilometer depth from the surface, within temperature gradients of 150°C to 300°C.
Minerals containing silver and gold can form deposits under these conditions, depending on the concentration of the metals in the brines and sudden changes in local pressure gradients, pH levels, and fluid flow dynamics. The alteration intensity of the Cerro Prieto deposits varies from weak to strongly pervasive textures, with the structure being most pronounced near larger veins. Silicification is generally extensive near mineralization, followed by sericite-illite-kaolinite assemblages.
The geological setting of the Esperanzas Deposit, classifies the gold-silver-bearing deposit as a low-sulfidation epithermal type.